Physical Quantity Sensor, Inertial Measurement Unit, And Method For Manufacturing Physical Quantity Sensor

ABSTRACT

Provided is a physical quantity sensor including: a movable body; a base body; and a lid body, in which the movable body is accommodated in a space between the base body and the lid body, the space is sealed with a melt portion obtained by melting a through hole provided in the lid body, the lid body and the melt portion contain silicon, and the melt portion has a continuous curved surface having unevenness.

This application is a divisional of U.S. patent application Ser. No.17/474,145 filed Sep. 14, 2021, which claims priority from JPApplication Serial Number 2020-154423, filed Sep. 15, 2020, thedisclosures of which are expressly incorporated by reference herein intheir entireties.

BACKGROUND 1. Technical Field

The present disclosure relates to a physical quantity sensor, aninertial measurement unit, and a method for manufacturing a physicalquantity sensor.

2. Related Art

An acceleration sensor, an angular velocity sensor, and the like arerealized by micro electro mechanical systems (MEMS). In the MEMS, amovable body is accommodated in a sealed space in a package. An airpressure in the sealed space is a pressure at which the movable bodyeasily functions.

A sealing method of a package is disclosed in US Patent ApplicationPublication NO. 2013/0074596. According to this, the package includes acap wafer as a lid body made of silicon. A through hole is provided inthe lid body. In a sealing step, the through hole is irradiated withlaser light, and a periphery of the through hole is melted, and thus thethrough hole is closed.

However, in the sealing method of a package of US Patent ApplicationPublication NO. 2013/0074596, there is a risk that a crack may occur inthe through hole provided in a lid portion. Specifically, when the laserlight is radiated, a temperature rapidly rises in the periphery of thesealing material and the through hole, and the sealing material ismelted. Although the sealing material solidifies when the radiation isstopped, since thermal expansion coefficients of the sealing materialand the lid portion are different from each other, thermal stressremains in the vicinity of the through hole which is close to thesealing material. Strain due to residual stress may occur, and there isrisk that the crack may be induced.

SUMMARY

A physical quantity sensor includes: a movable body; a base body; and alid body, in which the movable body is accommodated in a space betweenthe base body and the lid body, the space is sealed with a melt portionobtained by melting a through hole provided in the lid body, the lidbody and the melt portion contain silicon, and the melt portion has acontinuous curved surface having unevenness.

An inertial measurement unit includes the physical quantity sensor.

A method for manufacturing a physical quantity sensor includes: forminga through hole and a recess portion in a lid body containing silicon;configuring a movable body to be accommodated in a space between the lidbody and the base body; and irradiating the through hole and the recessportion with laser light to melt the through hole and the recess portionand seal the space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side sectional view showing a configuration of anangular velocity sensor according to a first embodiment.

FIG. 2 is a schematic plan view showing an angular velocity detectionelement.

FIG. 3 is a schematic diagram for describing an operation of the angularvelocity detection element.

FIG. 4 is a schematic diagram for describing the operation of theangular velocity detection element.

FIG. 5 is a schematic diagram for describing the operation of theangular velocity detection element.

FIG. 6 is a schematic diagram for describing the operation of theangular velocity detection element.

FIG. 7 is a schematic plan view of a main portion of a melt portion.

FIG. 8 is a schematic side sectional view of the main portion of themelt portion.

FIG. 9 is a schematic view for describing a method for manufacturing theangular velocity sensor.

FIG. 10 is a schematic view for describing the method for manufacturingthe angular velocity sensor.

FIG. 11 is a schematic plan view showing a shape of a second recessportion.

FIG. 12 is a schematic side sectional view showing the shape of thesecond recess portion.

FIG. 13 is a schematic view for describing the method for manufacturingthe angular velocity sensor.

FIG. 14 is a schematic view for describing the method for manufacturingthe angular velocity sensor.

FIG. 15 is a schematic view for describing the method for manufacturingthe angular velocity sensor.

FIG. 16 is a schematic view for describing the method for manufacturingthe angular velocity sensor.

FIG. 17 is a schematic side sectional view showing a configuration of anacceleration sensor according to a second embodiment.

FIG. 18 is a schematic plan view showing an acceleration detectionelement.

FIG. 19 is a schematic side sectional view of a main portion of a meltportion.

FIG. 20 is a schematic side sectional view showing a configuration of aninertial sensor according to a third embodiment.

FIG. 21 is a schematic view for describing a method for manufacturingthe inertial sensor.

FIG. 22 is a schematic view for describing the method for manufacturingthe inertial sensor.

FIG. 23 is a schematic view for describing the method for manufacturingthe inertial sensor.

FIG. 24 is a schematic view for describing the method for manufacturingthe inertial sensor.

FIG. 25 is a block diagram showing a configuration of a laser sealingdevice.

FIG. 26 is a schematic view for describing the method for manufacturingthe inertial sensor.

FIG. 27 is a schematic view for describing the method for manufacturingthe inertial sensor.

FIG. 28 is a schematic view for describing the method for manufacturingthe inertial sensor.

FIG. 29 is a schematic view for describing the method for manufacturingthe inertial sensor.

FIG. 30 is a schematic perspective view showing a configuration of aninertial measurement unit according to a fourth embodiment.

FIG. 31 is a schematic perspective view showing a configuration of asubstrate.

FIG. 32 is a schematic plan view of a main portion showing anarrangement of through holes and recess portions according to a fifthembodiment.

FIG. 33 is a schematic plan view of the main portion showing thearrangement of the through holes and the recess portions.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

In the present embodiment, an example of a physical quantity sensor anda method for manufacturing a characteristic physical quantity sensorwill be described. As shown in FIG. 1 , an angular velocity sensor 1 asa physical quantity sensor includes a base body 2. The base body 2 isprovided with an angular velocity detection element 3 as a movable body.A material of the base body 2 may be silicon, glass, quartz, or thelike.

A lid body 4 is installed on the base body 2. A material of the lid body4 is silicon. The lid body 4 is bonded to the base body 2 by a bondinglayer 5. However, the lid body 4 may be directly bonded to the base body2. A direction from the base body 2 toward the lid body 4 is defined asa Z direction. Planar shapes of the base body 2 and the lid body 4 arequadrangular when viewed from the Z direction. A direction in which oneside of the planar shape of the base body 2 extends is defined as an Xdirection, and a direction orthogonal to the X direction and the Zdirection is defined as a Y direction.

The lid body 4 includes a first recess portion 4 a on a base body 2side. The angular velocity detection element 3 is disposed in the firstrecess portion 4 a. As described above, the angular velocity sensor 1includes the lid body 4 that accommodates the angular velocity detectionelement 3 together with the base body 2. The angular velocity detectionelement 3 is accommodated in a space 6 between the base body 2 and thelid body 4. The angular velocity detection element 3 may be accommodatedin the space 6, and the first recess portion 4 a may not be provided onthe base body 2 side of the lid body as will be described later. Athrough hole 4 b is provided in the lid body 4. The lid body 4 includesa melt portion 4 c formed by melting the through hole 4 b. The meltportion 4 c seals the space 6 by closing the through hole 4 b. The meltportion 4 c is a part of the lid body 4 and contains silicon. Electrodepads 19 electrically coupled to the angular velocity detection element 3are disposed on the base body 2.

Although the through hole 4 b penetrates during a manufacturing processof the angular velocity sensor 1, the through hole 4 b is in a form of abag hole after being closed by the melt portion 4 c. A name of thethrough hole 4 b has a meaning that the through hole 4 b penetrates tothe middle of manufacturing the angular velocity sensor 1.

Next, the angular velocity detection element 3 will be described.

As shown in FIG. 2 , the angular velocity detection element 3 includes avibration system structure 104, drive fixed electrodes 130, detectionfixed electrodes 140, and fixing portions 150.

The vibration system structure 104 is integrally formed by, for example,processing a silicon substrate bonded to the base body 2. Accordingly, afine processing technique used for manufacturing a silicon semiconductordevice can be applied, and a size of the vibration system structure 104can be reduced.

The vibration system structure 104 is supported by the fixing portions150 fixed to the base body 2, and is disposed in a manner of beingseparated from the base body 2. The vibration system structure 104includes a first vibrating body 106 and a second vibrating body 108. Thefirst vibrating body 106 and the second vibrating body 108 are coupledto each other along an X axis.

The first vibrating body 106 and the second vibrating body 108 haveshapes that are symmetrical with respect to a boundary line B betweenthe first vibrating body 106 and the second vibrating body 108. Theboundary line B is a straight line along a Y axis. A configuration ofthe first vibrating body 106 will be described, and a description of theconfiguration of the second vibrating body 108 will be omitted.

The first vibrating body 106 includes a drive unit 110 and a detectionunit 120. The drive unit 110 includes a drive support portion 112, drivespring portions 114, and drive movable electrodes 116.

The drive support portion 112 has, for example, a frame shape, and thedetection unit 120 is disposed inside the drive support portion 112. Thedrive support portion 112 includes a first extending portion 112 aextending along the X axis and a second extending portion 112 bextending along the Y axis.

The drive spring portion 114 is disposed outside the drive supportportion 112. One end of the drive spring portion 114 is coupled to thevicinity of a corner portion of the drive support portion 112. Thecorner portion of the drive support portion 112 is a coupling portionbetween the first extending portion 112 a and the second extendingportion 112 b. Another end of the drive spring portion 114 is coupled tothe fixing portion 150.

In the first vibrating body 106, four drive spring portions 114 areprovided. The first vibrating body 106 is supported by four fixingportions 150. The fixing portions 150 on the boundary line B between thefirst vibrating body 106 and the second vibrating body 108 may not beprovided. The first vibrating body 106 and the second vibrating body 108may be directly coupled using an elastically deformable couplingportion.

The drive spring portion 114 has a shape extending along the X axiswhile reciprocating along the Y axis. The plurality of drive springportions 114 are symmetrically provided with respect to a virtual line(not shown) along the X axis passing through a center of the drivesupport portion 112 and a virtual line (not shown) along the Y axispassing through the center of the drive support portion 112. By formingthe drive spring portion 114 into the above-described shape, the drivespring portion 114 can be inhibited from being deformed in a Y-axisdirection and a Z-axis direction, and the drive spring portion 114 canbe smoothly extended and contracted in an X-axis direction, which is avibration direction of the drive unit 110. With the expansion andcontraction of the drive spring portion 114, the drive support portion112 can be vibrated along the X axis.

Outside the drive support portion 112, the drive movable electrodes 116are coupled to the drive support portion 112. The drive movableelectrode 116 is coupled to the first extending portion 112 a of thedrive support portion 112.

The drive fixed electrode 130 is disposed on an outer side of the drivesupport portion 112. The drive fixed electrode 130 is fixed on the basebody 2. A plurality of drive fixed electrodes 130 are provided andarranged in a manner of facing the drive movable electrode 116. Thedrive fixed electrode 130 has a comb shape. The drive movable electrode116 has protruding portions 116 a that can be inserted between combteeth of the drive fixed electrode 130. By reducing a distance betweenthe drive fixed electrode 130 and the protruding portion 116 a, anelectrostatic force acting between the drive fixed electrode 130 and thedrive movable electrode 116 can be increased.

When a voltage is applied to the drive fixed electrode 130 and the drivemovable electrode 116, an electrostatic force can be generated betweenthe drive fixed electrode 130 and the drive movable electrode 116.Accordingly, the drive spring portion 114 expands and contracts alongthe X axis, and the drive support portion 112 of the drive unit 110 canbe vibrated along the X axis.

The detection unit 120 is coupled to the drive unit 110. In the shownexample, the detection unit 120 is disposed inside the drive supportportion 112. The detection unit 120 may include a detection supportportion 122, detection spring portions 124, and detection movableelectrodes 126. Although not shown, if the detection unit 120 is coupledto the drive unit 110, the detection unit 120 may be disposed on anouter side of the drive support portion 112.

The detection support portion 122 has, for example, a frame shape. Inthe shown example, the detection support portion 122 includes thirdextending portions 122 a extending along the X axis and fourth extendingportions 122 b extending along the Y axis.

The detection spring portion 124 is disposed on an outer side of thedetection support portion 122. The detection spring portion 124 couplesthe detection support portion 122 and the drive support portion 112.More specifically, one end of the detection spring portion 124 iscoupled to the vicinity of a corner portion of the detection supportportion 122. The corner portion of the detection support portion 122 isa coupling portion between the third extending portion 122 a and thefourth extending portion 122 b. Another end of the detection springportion 124 is coupled to the first extending portion 112 a of the drivesupport portion 112.

The detection spring portion 124 has a shape extending along the Y axiswhile reciprocating along the X axis. In the shown example, fourdetection spring portions 124 are provided in the first vibrating body106. The plurality of detection spring portions 124 are symmetricallyprovided with respect to a virtual line (not shown) along the X axispassing through a center of the detection support portion 122 and avirtual line (not shown) along the Y axis passing through the center ofthe detection support portion 122. By forming the detection springportion 124 into a shape as described above, deformation of thedetection spring portion 124 in the X-axis direction and the Z-axisdirection can be inhibited, and the detection spring portion 124 can besmoothly expanded and contracted in the Y-axis direction which is thevibration direction of the detection unit 120. With the expansion andcontraction of the detection spring portion 124, the detection supportportion 122 of the detection unit 120 can be vibrated along the Y axis.The number of the detection spring portions 124 is not particularlylimited as long as the detection spring portions 124 can vibrate thedetection support portion 122 along the Y axis.

The detection movable electrode 126 is disposed inside the detectionsupport portion 122 in a manner of being coupled to the detectionsupport portion 122. In the shown example, the detection movableelectrode 126 extends along the X-axis, and is coupled to the two fourthextending portions 122 b of the detection support portion 122.

The detection fixed electrode 140 is disposed on the inner side of thedetection support portion 122. The detection fixed electrode 140 isfixed on the base body 2. In the shown example, the plurality ofdetection fixed electrodes 140 are provided, and are arranged in amanner of facing each other with the detection movable electrode 126interposed therebetween.

The numbers and shapes of the detection movable electrodes 126 and thedetection fixed electrodes 140 are not particularly limited as long as achange in capacitance between the detection movable electrode 126 andthe detection fixed electrode 140 can be detected.

Next, an operation of the angular velocity detection element 3 will bedescribed. FIGS. 3 to 6 are schematic views for describing the operationof the angular velocity detection element 3 of the angular velocitysensor 1 according to the present embodiment. For convenience, in FIGS.3 to 6 , parts of the angular velocity detection element 3 are shown ina simplified manner.

When a voltage is applied to the drive fixed electrode 130 and the drivemovable electrode 116, an electrostatic force can be generated betweenthe drive fixed electrode 130 and the drive movable electrode 116.Accordingly, as shown in FIGS. 3 and 4 , the drive spring portion 114can be expanded and contracted along the X axis, and the drive unit 110can be vibrated along the X axis.

More specifically, a first alternating voltage is applied between thedrive movable electrode 116 and the driving fixed electrode 130 of thefirst vibrating body 106, and a second alternating voltage whose phasedeviated by 180 degrees from that of the first alternating voltage isapplied between the drive movable electrode 116 and the driving fixedelectrode 130 of the second vibrating body 108. Accordingly, a firstdriving unit 110 a of the first vibrating body 106 and a second drivingunit 110 b of the second vibrating body 108 can be vibrated along the Xaxis in opposite phases and at a predetermined frequency. That is, thefirst driving unit 110 a and the second driving unit 110 b coupled toeach other along the X axis vibrate in opposite phases to each otheralong the X axis. The vibration is referred to as a first vibration. Forexample, first, as shown in FIG. 3 , the first driving unit 110 a isdisplaced in an al direction, and the second driving unit 110 b isdisplaced in an α2 direction opposite to the α1 direction. Next, asshown in FIG. 4 , the first driving unit 110 a is displaced in the α2direction, and the second driving unit 110 b is displaced in the aldirection. The first driving unit 110 a and the second driving unit 110b repeat the operation. In this way, the first driving unit 110 a andthe second driving unit 110 b vibrate in mutually opposite phases.

Since the detection unit 120 is coupled to the drive unit 110, thedetection unit 120 also vibrates along the X axis in accordance with thevibration of the drive unit 110. That is, the first vibrating body 106and the second vibrating body 108 vibrate in mutually opposite phasesalong the X axis. The vibration is referred to as a first vibration.

As shown in FIGS. 5 and 6 , when an angular velocity co around a Z axisis applied to the angular velocity detection element 3 in a state wherethe first driving unit 110 a and the second driving unit 110 b performthe first vibration, the Coriolis force acts, and the detection unit 120is displaced along the Y axis. That is, a first detection unit 120 acoupled to the first driving unit 110 a and a second detection unit 120b coupled to the second driving unit 110 b are displaced in mutuallyopposite directions along the Y axis by the first vibration and theCoriolis force. For example, first, as shown in FIG. 5 , the firstdetection unit 120 a is displaced in a β1 direction, and the seconddetection unit 120 b is displaced in a β2 direction opposite to the β1direction. Next, as shown in FIG. 6 , the first detection unit 120 a isdisplaced in the β2 direction, and the second detection unit 120 b isdisplaced in the β1 direction. The first detection unit 120 a and thesecond detection unit 120 b repeat the operation while receiving theCoriolis force.

By displacing the first detection unit 120 a and the second detectionunit 120 b along the Y axis, a distance L between the detection movableelectrode 126 and the detection fixed electrode 140 changes. Therefore,capacitance between the detection movable electrode 126 and thedetection fixed electrode 140 changes. In the angular velocity detectionelement 3, by applying a voltage to the detection movable electrode 126and the detection fixed electrode 140, a change amount in capacitancebetween the detection movable electrode 126 and the detection fixedelectrode 140 can be detected, and the angular velocity ω around the Zaxis can be obtained.

Next, the melt portion 4 c of the lid body 4 will be described. As shownin FIGS. 7 and 8 , when viewed from the Z direction, the melt portion 4c has a substantially circular shape and overlaps with the through hole4 b. The melt portion 4 c has a continuous curved surface 4 d havingunevenness.

According to the configuration, since the through hole 4 b is sealed,the space 6 is sealed by the lid body 4. Laser light is radiated, andthe melt portion 4 c is formed. The melt portion 4 c is a polycrystal,and the periphery of the melt portion 4 c is a single crystal. The meltportion 4 c and the periphery of the melt portion 4 c have differentcrystal structures. In a place where the crystal structure rapidlychanges, a change in residual stress is large, and a crack is likely tooccur. When the melt portion 4 c is provided with a continuous curvedsurface 4 d having unevenness, the crystal structure is gently changed.Therefore, since the change in residual stress is gentle, an occurrenceof cracks can be inhibited.

The lid body 4 is a single crystal, and the melt portion 4 c ispolycrystalline. Specifically, the lid body 4 other than the meltportion 4 c is a single crystal. According to the configuration, thepolycrystalline melt portion 4 c can be easily formed by irradiating thelid body 4, which is a single crystal, with laser light and heating thelid body 4.

Although a dimension of the lid body 4 is not particularly limited, inthe present embodiment, for example, the thickness of the lid body 4 is180 μm. A depth of the first recess portion 4 a is 50 μm. Therefore, athickness of the lid body 4 in the first recess portion 4 a is 130 μm.

A diameter of the through hole 4 b is 10 μm to 30 μm. A melt portionuneven depth 7, which is the depth of the melt portion 4 c, ispreferably 10 μm or more and 50 μm or less. The melt portion unevennessdepth 7 indicates a length from a bottom of a recessed portion of themelt portion 4 c to a protruding portion. When a beam condensingdiameter of a laser light is 200 μm, a melt portion diameter 8 of themelt portion 4 c is 140 μm to 220 μm. That is, a size is 70 to 110% ofthe beam condensing diameter. A length from a second surface 4 f to anend surface of the through hole 4 b is set as a melt portion depth 17.The melt portion depth 17 is set to D, and the melt portion diameter 8is denoted by L. A D/L ratio, which is a depth diameter ratio obtainedby dividing the melt portion depth 17 by the melt portion diameter 8, ispreferably 0.5 or more and 3.0 or less.

The angular velocity detection element 3 always vibrates at a constantfrequency, and the air pressure of the space 6 is reduced in order toreduce a resistance at the time of vibration. In order to stably vibratethe angular velocity detection element 3 in a state where a Q value ofthe vibration is high, the air pressure of the space 6 is 0.1 Pa to 10Pa.

When a crack is formed in the lid body 4, a leak path is formed betweenthe space 6 and an outside air. The air pressure in the space 6 is theatmospheric pressure. At the time, a vibration of the angular velocitydetection element 3 is attenuated, and a detection sensitivity of theangular velocity detection element 3 decreases.

Next, a method for manufacturing the angular velocity sensor 1 will bedescribed. In FIG. 9 , a recess portion 2 a is formed in a base body 2which is an insulating base body, and a metal wiring (not shown) isformed. The base body 2 may be made of glass, quartz, or the like. Inthe present embodiment, for example, Tempax (registered trademark) glassis used. When glass is used for the base body 2, the recess portion 2 ais formed by wet etching with HF. HF represents hydrogen fluoride. Theangular velocity detection element 3 is formed by anodic bonding thesilicon substrate, and then performing vertical processing by a Boschprocess. By alloying a bump and silicon on a metal wiring (not shown) byheat treatment, a good electrical coupling can be obtained. If platinumis used as an outermost surface of the metal wiring, a good silicidealloy may be formed. A method of forming the angular velocity detectionelement 3 is known, and a detailed description thereof will be omitted.

As shown in FIG. 10 , a substrate which is a material of the lid body 4is prepared. The substrate of the lid body 4 has a (100) plane made ofsilicon. The first recess portion 4 a having a depth of about 30 μm to50 μm is formed in a first surface 4 e by the Bosch process. In the lidbody 4, a surface on a side opposite to the first surface 4 e isreferred to as the second surface 4 f. The through hole 4 b and secondrecess portions 4 g as recesses are further formed on the second surface4 f of the lid body 4 by the Bosch process. The second recess portion 4g is also referred to as a dummy pattern. An etching depth of thethrough hole 4 b and the second recess portion 4 g may be controlled byusing a micro loading effect or by adjusting a thickness of a mask.Next, the bonding layer 5 is formed on the lid body 4. The bonding layer5 is printed on an entire wafer on a lid body 4 side using a screenprinting technique. The bonding layer 5 may be disposed on the base body2. In this way, the through hole 4 b and the second recess portion 4 gare formed from the second surface 4 f in the lid body 4 containingsilicon.

As shown in FIG. 11 , the second recess portion 4 g is constituted by afirst groove 9 and a second groove 10 which are concentric with thethrough hole 4 b in a plan view seen from the Z direction. A groovewidth 11 of the first groove 9 and the second groove 10 is preferably 10μm or more and 20 μm or less. An inter-groove distance 12 of the firstgroove 9 and the second groove 10 is preferably 10 μm or more and 20 μmor less.

As shown in FIG. 12 , a groove depth 13 of the first groove 9 and thesecond groove 10 is 20 μm or more and 40 μm or less. The through hole 4b and the second recess portion 4 g are formed by using a known Boschprocess method. The Bosch process method enables etching with a highaspect ratio.

The groove depth 13 may be controlled by changing the number of times ofetching of the through hole 4 b and the second recess portion 4 g. Forexample, a length of the through hole 4 b is 130 μm, and the groovedepth 13 is 30 μm. The digging depth in one etching cycle is assumed tobe 1 μm. By performing 100 cycles of etching, the through hole 4 b isdug by 100 μm. Next, 30 cycles of etching are added to dig the throughhole 4 b and the second recess portion 4 g in parallel by 30 μm. By theabove method, the through hole 4 b penetrates, and the groove depth 13is 30 μm.

As shown in FIG. 13 , the lid body 4 and the base body 2 are bonded toeach other. The bonding is performed by applying pressure and heating.The pressurization is performed in a range of 10 to 1000 kPa, and theheating is performed in a range of 250 to 500° C. The atmosphere may bean inert gas such as nitrogen or argon, and the air pressure may bevacuum, an atmospheric pressure, or a positive pressure. The lid body 4is bonded to the base body 2 by using a glass frit material serving asthe bonding layer 5. Although in the present embodiment, frit bondingusing glass frit is used, anodic bonding, direct bonding, metal eutecticbonding, or plasma activation bonding may be used. The through hole 4 band the second recess portion 4 g may be formed after the bonding layer5 is bonded. The angular velocity detection element 3 is accommodated inthe space 6 between the provided base body 2 and the lid body 4.

As shown in FIG. 14 , degassing processing is performed by vacuumheating processing. Specifically, heating is performed at 300° C. orhigher and 100 Pa or lower for several hours. The gas in the space 6 istaken out from the through hole 4 b to an outside. In the presentembodiment, for example, a pressure inside a decompression chamber isreduced to 1 Pa. An inside of the chamber has a reduced-pressureatmosphere. Next, hydrophobic treatment is performed such that moisturedoes not adhere to the space 6. In the hydrophobic treatment, HMDS,which is a silane coupling agent, was used. HMDS representshexamethyldisilazane. By such a hydrophobic treatment, a moisturecontent of the space 6 can be reduced to 100 ppm or less. By preventingan entry of moisture, the space 6 can be maintained in a high vacuumstate. Therefore, the angular velocity detection element 3 can be stablyvibrated in a state where the Q value of the vibration is high.

Next, as shown in FIG. 15 , the second recess portions 4 g and thethrough hole 4 b are irradiated with the laser light 14. In a state inwhich the base body 2 and the lid body 4 are heated and the temperatureof the lid body 4 is increased, the through hole 4 b and the secondrecess portion 4 g are simultaneously irradiated with the laser light14. The laser light 14 is emitted from a laser light source 15 andcondensed by a condensing optical system 16. A diameter of a condensingportion 14 a on which the laser light 14 is condensed is 100 μm to 200μm. In the second recess portion 4 g, a diffraction of the laser light14 can be promoted, and the second recess portion 4 g can be melted bylower energy. Therefore, an amount of dross, debris, and the like issmall, and cracks are unlikely to occur. Since a temperature of the lidbody 4 is increased, the second recess portion 4 g can be melted bylower energy. A power of the laser light 14 may be 0.5 to 1.0 times thepower at which the flat second surface 4 f is melted. The second recessportion 4 g and the through hole 4 b are irradiated with the laser light14, the second recess portion 4 g and the through hole 4 b are melted,and the space 6 is sealed. The radiation of the laser light 14 isperformed under a reduced-pressure atmosphere in a chamber including awindow portion transparent to the laser light 14. When the laser light14 is radiated, the lid body 4 is heated via the base body 2.

A wavelength of the laser light 14 is 1070 nm to 1100 nm, which is closeto a silicon band gap. Since the material of the lid body 4 is silicon,a laser having a wavelength with a small light absorption coefficientwas selected such that an ablation phenomenon did not occur in a laserirradiation process. A wavelength having a small light absorptioncoefficient is a laser having a wavelength in the vicinity of the bandgap wavelength of silicon or a wavelength longer than the band gapwavelength. When the wavelength is 800 nm or more, the light absorptioncoefficient can be set to 300 cm⁻¹ or less. When a laser having such awavelength is selected, silicon can be melted by thermal processing. Inthe present embodiment, for example, an yttrium aluminum garnet (YAG)laser is used, and the wavelength of the laser light 14 is set to about1064 nm.

As shown in FIG. 12 , the laser light 14 is diffracted by the secondrecess portion 4 g, and laser melting can be performed more efficiently.For example, when a laser irradiation energy capable of melting a flatsurface is set to E0, good melting can be performed by an energy amountof 0.1 to 0.5×E0. Therefore, hole sealing by which debris and dross areinhibited can be performed.

According to the method, the through hole 4 b and the second recessportion 4 g are formed in the lid body 4. The through hole 4 b isirradiated with the laser light 14. The lid body 4 is melted to closethe through hole 4 b. Since a part of the laser light 14 is diffractedin the second recess portion 4 g, the laser light 14 travels in multipledirections in the periphery of the through hole 4 b. The laser light 14is absorbed by silicon at a shallow location close to a surface of thelid body 4. In the through hole 4 b, a temperature near the surface ofthe lid body 4 is high, and the temperature gradually decreases as adistance from the surface increases. As a distance from the through hole4 b increases, the temperature gradually decreases.

The melt portion 4 c is a polycrystal, and the periphery of the meltportion 4 c is a single crystal. Although the melt portion 4 c and theperiphery of the melt portion 4 c have different crystal structures,thermal expansion coefficients thereof are substantially the same. Inthe through hole 4 b, a crystal structure gradually changes as thedistance from the surface of the lid body 4 increases. As the distancefrom the through hole 4 b increases, the crystal structure graduallychanges. Therefore, since the change in residual stress is gentle, theoccurrence of cracks can be inhibited.

When the laser light 14 is radiated, the angular velocity sensor 1 is ina reduced-pressure atmosphere inside the chamber including a windowportion transparent with respect to the laser light 14, and the lid body4 is heated via the base body 2. According to the above method, sincethe through hole 4 b is sealed in a reduced-pressure atmosphere, thespace 6 for accommodating the angular velocity detection element 3 issealed in a reduced-pressure state. Since a thermal conductivity of anatmosphere gas is low in the reduced-pressure atmosphere, thetemperature of the lid body 4 decreases. In general, a thermalconductivity of gas greatly changes at 100 to 1,000 Pa. Therefore, sincea pressure in the space 6, at which the angular velocity detectionelement 3 is easy to operate, is 0.1 to 10 Pa, if the lid body 4 isheated via the base body 2, an efficiency is significantly reduced. Whenthe temperature of the lid body 4 decreases, the lid body 4 is difficultto melt, and stronger laser radiation energy is required. This causesdebris and dross. In this method, since the lid body 4 is sufficientlyheated to 300° C. or higher, the lid body 4 can be reliably melted toseal the through hole 4 b.

Next, as shown in FIG. 16 , at least one side of the lid body 4 is cutoff by a dicing blade 18. The above makes it possible to expose theelectrode pads 19 disposed on the base body 2. That is, wire bonding ispossible. At the time, the base body 2 and the bonding layer 5 are notcut. Therefore, the space 6 can maintain good airtightness. Finally,four sides of the base body 2 are divided, and the angular velocitysensor 1 is taken out. Through the above steps, the angular velocitysensor 1 is completed.

Second Embodiment

The present embodiment is different from the first embodiment in that,an acceleration detection element is provided instead of the angularvelocity detection element 3. Same components as those of the firstembodiment are denoted by the same reference numerals, and redundantdescription thereof will be omitted.

As shown in FIG. 17 , an acceleration sensor 21 as a physical quantitysensor includes the base body 2. The base body 2 is provided with anacceleration detection element 22 as the movable body.

A lid body 23 is installed on the base body 2. The lid body 23 is bondedto the base body 2 by the bonding layer 5. The lid body 23 includes afirst recess portion 23 a on a base body 2 side. The accelerationdetection element 22 is disposed in the first recess portion 23 a. Asdescribed above, the acceleration sensor 21 includes the lid body 23that accommodates the acceleration detection element 22 together withthe base body 2. The acceleration detection element 22 is accommodatedin the space 6 between the base body 2 and the lid body 23. A throughhole 23 b is provided in the lid body 23. The lid body 23 includes amelt portion 23 c formed by melting the through hole 23 b. The meltportion 23 c closes the through hole 23 b, and thus seals the space 6.The melt portion 23 c includes a continuous curved surface 23 d havingunevenness.

Next, the acceleration detection element 22 will be described.

The acceleration detection element 22 shown in FIG. 18 is anacceleration sensor element that detects acceleration Ax in the Xdirection. The base body 2 is provided with a first mount portion 76 anda second mount portion 77, and supports the acceleration detectionelement 22. The acceleration detection element 22 includes a movableportion 71, spring portions 72, fixed portions 73, first fixed detectionelectrodes 74, and second fixed detection electrodes 75.

The movable portion 71 includes a base portion 71 a extending in the Xdirection and movable detection electrodes 71 b which are a plurality ofmovable electrodes protruding from the base portion 71 a to both sidesin the Y direction. The movable portion 71 is coupled to the fixingportions 73 via the spring portions 72 at both end portions of the baseportion 71 a. The fixing portion 73 is fixed to the first mount portion76 protruding from the base body 2. Accordingly, the movable portion 71can be displaced in the X direction relative to the fixing portion 73.The first fixed detection electrode 74 and the second fixed detectionelectrode 75, which are fixed electrodes, are fixed to the second mountportion 77 protruding from the base body 2, and are provided with themovable detection electrode 71 b interposed therebetween.

The first fixed detection electrode 74 and the second fixed detectionelectrode 75 are disposed between the two movable detection electrodes71 b. When the movable portion 71 is displaced in a positive Xdirection, the movable detection electrode 71 b approaches the firstfixed detection electrode 74 and is separated from the second fixeddetection electrode 75. When the movable portion 71 is displaced in anegative X direction, the movable detection electrode 71 b approachesthe second fixed detection electrode 75 and is separated from the firstfixed detection electrode 74.

The movable detection electrode 71 b of the movable portion 71 iselectrically coupled to a first terminal via a wiring provided on thebase body 2 and a contact 68. The first fixed detection electrode 74 anda second terminal are electrically coupled to each other via the wiring.The second fixed detection electrode 75 and a third terminal areelectrically coupled to each other via the wiring. Among the movabledetection electrode 71 b of the movable portion 71, the first fixeddetection electrode 74, and the second fixed detection electrode 75, apredetermined voltage is applied via the first terminal, the secondterminal, and the third terminal, and capacitances are respectivelyformed between the movable detection electrode 71 b, and the first fixeddetection electrode 74 and the second fixed detection electrode 75. Eachof the first terminal, the second terminal, and the third terminal isone of the electrode pads 19.

The acceleration detection element 22 can detect the acceleration Ax inthe following manner. When the acceleration Ax is applied to theacceleration detection element 22, the movable portion 71 is displacedin the X direction while elastically deforming the spring portion 72based on a magnitude of the acceleration Ax. When the movable portion 71is displaced, a gap between the movable detection electrode 71 b and thefirst fixed detection electrode 74 and a gap between the movabledetection electrode 71 b and the second fixed detection electrode 75change, and accordingly, the capacitance therebetween changes.Therefore, the acceleration Ax can be detected based on the changeamount in the capacitance.

In FIG. 17 , a through hole 23 b is provided in the lid body 23, and anatmospheric pressure of the space 6 accommodating the accelerationdetection element 22 can be adjusted. By adjusting the atmosphericpressure in the space 6, a damping effect of converging an amplitude ofunnecessary vibration of the acceleration detection element 22 can beobtained. A damping effect must be sufficiently secured over a productlife. Specifically, a sealing pressure is preferably 10,000 to 150,000Pa using an inert gas such as nitrogen or argon. In this manner, afterthe pressure in the space 6 is adjusted to a pressure at which theacceleration detection element 22 is easy to operate, the through hole23 b is sealed by using the laser light 14. When the laser irradiationenergy capable of melting the flat surface is set to E0, good meltingcan be performed by the energy amount of 0.1 to 0.5×E0.

Also in a sealing step of sealing the acceleration detection element 22,the base body 2 and the lid body 23 are heated by a heater. A heatingtemperature of the lid body 23 is preferably lower than that of theangular velocity detection element 3. The temperature is preferably 200°C. to 300° C., which is lower than that of the first embodiment. In thesealing step of the acceleration detection element 22, as describedabove, the pressure of the space 6 is set to a pressure of 10,000 to150,000 Pa, which is higher than that when the angular velocitydetection element 3 is sealed, and thus the thermal conductivity of theatmospheric gas is relatively good. Therefore, even when a temperatureis set to be lower than that of the angular velocity detection element3, the through hole 23 b can be satisfactorily melted. Further, since atemperature of the lid body 23 is higher by laser melting, it ispreferably to set the temperature to be slightly lower. After all lasermelting steps are completed, the acceleration sensor 21 is returned to aroom temperature, and then the acceleration sensor 21 is taken out fromthe chamber.

Similarly to the angular velocity sensor 1, the acceleration sensor 21can suppress the occurrence of cracks in the through hole 23 b.Therefore, the acceleration sensor 21 with high reliability can bemanufactured.

Next, the melt portion 23 c of the lid body 23 will be described. Asshown in FIG. 19 , when viewed from the Z direction, the melt portion 23c has a substantially circular shape and overlaps with the through hole23 b. The melt portion 23 c includes the continuous curved surface 23 dhaving unevenness.

Although a dimension of the lid body 23 is not particularly limited, inthe present embodiment, for example, a thickness of the lid body 23 is180 μm. A depth of the first recess portion 23 a is 50 μm. Therefore,the thickness of the lid body 23 in the first recess portion 23 a is 130μm.

The diameter of the through hole 23 b is preferably 10 μm to 30 μm. Themelt portion unevenness depth 7, which is the depth of the melt portion23 c, is 10 μm or more and 50 μm or less. The melt portion unevennessdepth 7 indicates a length from a bottom of a recessed part of the meltportion 23 c to the protruding part. When a beam condensing diameter ofa laser light is 200 μm, a melt portion diameter of the melt portion 23c is 140 μm to 220 μm. That is, a size is 70 to 110% of the beamcondensing diameter. A length from a second surface 23 f to an endsurface of the through hole 23 b is defined as a melt portion depth 17.The melt portion depth 17 is set to D, and the melt portion diameter 8is set to L. A D/L ratio, which is a depth diameter ratio obtained bydividing the melt portion depth 17 by the melt portion diameter 8, ispreferably 0.01 or more and 0.5 or less.

Third Embodiment

The present embodiment is different from the first embodiment and thesecond embodiment in that the angular velocity detection element 3 andthe acceleration detection element 22 are installed in the physicalquantity sensor. Same components as those in the first embodiment andthe second embodiment are denoted by the same reference numerals, andredundant description thereof will be omitted.

As shown in FIG. 20 , an inertial sensor 81 as a physical quantitysensor includes a base body 82. The base body 82 includes a siliconsubstrate 82 a, a silicon oxide layer 82 b, and a polycrystallinesilicon layer 82 c. The silicon oxide layer 82 b is stacked on thesilicon substrate 82 a. The polycrystalline silicon layer 82 c isstacked on the silicon oxide layer 82 b. The angular velocity detectionelement 3 and the acceleration detection element 22 are provided on thesilicon oxide layer 82 b.

The inertial sensor 81 includes a lid body 83 that accommodates theangular velocity detection element 3 and the acceleration detectionelement 22 together with a base body 82. The lid body 83 is bonded tothe base body 82 via a bonding layer 86. The angular velocity detectionelement 3 is accommodated in a first space 84 as a space between thebase body 82 and the lid body 83. The acceleration detection element 22is accommodated in a second space 85 as a space between the base body 82and the lid body 83. At the time, no recess portion is provided on asurface of the lid body 83 facing the angular velocity detection element3 and the acceleration detection element 22.

The lid body 83 is provided with a first through hole 83 a as a throughhole and a second through hole 83 b as a through hole. The lid body 83includes a first melt portion 83 c as a melt portion obtained by meltingthe first through hole 83 a. The first melt portion 83 c seals the firstspace 84 by closing the first through hole 83 a. The lid body 83includes a second melt portion 83 d as a melt portion obtained bymelting the second through hole 83 b. The second melt portion 83 d sealsthe second space 85 by closing the second through hole 83 b. A partitionwall 87 is disposed between the first space 84 and the second space 85.

The first through hole 83 a and the first melt portion 83 c correspondto the through hole 4 b and the melt portion 4 c according to the firstembodiment, respectively. A shape of the first melt portion 83 c issubstantially the same as that of the melt portion 4 c. The first space84 and the angular velocity detection element 3 are substantially thesame as the space 6 and the angular velocity detection element 3according to the first embodiment, respectively. The air pressure in thefirst space 84 is substantially the same as the air pressure in thespace 6 according to the first embodiment.

The second through hole 83 b and the second melt portion 83 d correspondto the through hole 23 b and the melt portion 23 c according to thesecond embodiment, respectively. A shape of the second melt portion 83 dis substantially the same as that of the melt portion 23 c. The secondspace 85 and the acceleration detection element 22 are substantially thesame as the space 6 and the acceleration detection element 22 accordingto the second embodiment, respectively. The air pressure in the secondspace 85 is substantially the same as the air pressure in the space 6according to the second embodiment. A reason why depths of the firstmelt portion 83 c and the second melt portion 83 d are different fromeach other is that laser irradiation energies are different from eachother.

Next, a method for manufacturing the inertial sensor 81 will bedescribed.

In FIG. 21 , the silicon substrate 82 a is prepared. The silicon oxidelayer 82 b as a sacrificial layer and the polycrystalline silicon layer82 c as an element layer are formed on the silicon substrate 82 a. Alower electrode layer (not shown) may be formed under the silicon oxidelayer 82 b. At the time, silicon nitride which is to be an etching stoplayer is formed on a lower surface. A thickness of the silicon oxidelayer 82 b is 2 μm or less, and a thickness of the polycrystallinesilicon layer 82 c is about 15 μm to 30 μm. A sputtering method, a vapordeposition method, or a CVD method is used to form the layers.Patterning is performed by a photolithography method, and the angularvelocity detection element 3 and the acceleration detection element 22are formed by using the Bosch method. At this time, the polycrystallinesilicon layer 82 c fixed to the silicon substrate 82 a serving as a partof the partition wall is left between the elements, such that the firstspace 84 and the second space 85 do not communicate with each other.Then, the silicon oxide layer 82 b is released by an HF vapor. The basebody 82 is provided with a plurality of physical quantity sensors suchas the angular velocity detection element 3 and the accelerationdetection element 22.

In FIG. 22 , a substrate 83 m as a material of the lid body 83 isprepared. The substrate 83 m has a (100) plane made of silicon. Asurface of the substrate 83 m opposite to the base body 82 is referredto as a second surface 83 f. A first through hole 83 a, a second throughhole 83 b, a third recess portion 83 g, and a fourth recess portion 83 hare formed in the second surface 83 f by the Bosch process. The thirdrecess portion 83 g and the fourth recess portion 83 h correspond to thesecond recess portion 4 g according to the first embodiment.

Etching depths of the first through hole 83 a, the second through hole83 b, the third recess portion 83 g and the fourth recess portion 83 hmay be controlled by using a micro loading effect or by adjusting thethickness of the mask. Next, the bonding layer 86 is formed on thesubstrate 83 m. Although the bonding layer 86 is printed on an entirewafer on a substrate 83 m side using a screen printing technique, thebonding layer 86 may be formed on a polycrystalline silicon layer 82 cside of the base body 82. The bonding layer 86 may be made of a lowmelting point alloy such as AlGe. In order to separate a sealingatmosphere between the first space 84 and the second space 85, thebonding layer 86 is also formed in a partition wall 87 portion.

A plurality of first spaces 84 and a plurality of second spaces 85 areprovided between the base body 82 and the substrate 83 m. The firstspace 84 is provided corresponding to at least one angular velocitydetection element 3. The first through hole 83 a and the third recessportion 83 g are provided corresponding to one first space 84. Thesecond space 85 is provided corresponding to at least one accelerationdetection element 22. The second through hole 83 b and the fourth recessportion 83 h are provided corresponding to one second space 85.Therefore, as shown in FIG. 28 , a plurality of first through holes 83 aare provided in the substrate 83 m. As shown in FIG. 28 , a plurality ofsecond through holes 83 b are provided in the substrate 83 m.

In FIG. 23 , the substrate 83 m and the base body 82 are bonded to eachother by pressurization and heating. A pressure at the time of bondingis 10 kPa to 1000 kPa. Heating at the time of bonding is performed in arange of 250° C. to 500° C. The atmosphere at the time of bonding may bean atmosphere of an inert gas such as nitrogen gas or argon gas, and maybe a vacuum, an air pressure, or a positive pressure. The substrate 83 mis bonded to the polycrystalline silicon layer 82 c using an AlGematerial to be the bonding layer 86. Although in the present embodiment,metal eutectic bonding using an AlGe material is used, anodic bonding,direct bonding, glass frit bonding, or plasma activation bonding may beused. The first through hole 83 a, the second through hole 83 b, thethird recess portion 83 g, and the fourth recess portion 83 h may beformed after the substrate 83 m and the base body 82 are bonded to eachother. A substrate to which the base body 82 and the substrate 83 m arebonded is referred to as a bonded substrate 98.

In FIG. 24 , degassing treatment is performed by vacuum heatingtreatment. Specifically, heating is performed at a temperature of 250°C. to 300° C. and an air pressure of 100 Pa or less for several hours. Agas in the first space 84 is taken out from the first through hole 83 ato an outside. A gas in the second space 85 is taken out from the secondthrough hole 83 b to the outside.

Next, hydrophobic treatment of the first space 84 and the second space85 is performed. In the hydrophobic treatment, HMDS, which is a silanecoupling agent, was used. By such a hydrophobic treatment, a moisturecontent of the first space 84 and the second space 85 can be reduced to100 ppm or less. Therefore, the angular velocity detection element 3 andthe acceleration detection element 22 can be operated favorably withoutbeing affected by a fluctuation of an atmospheric gas pressure due tomoisture.

A laser sealing device 88 as shown in FIG. 25 is prepared. The lasersealing device 88 includes a chamber 89. The laser sealing device 88includes a rotary pump 90 and a turbo-molecular pump 91 thatdepressurize an inside of the chamber 89. An XY stage 93 for moving anobject to be processed 92 is disposed inside the chamber 89. The XYstage 93 has a role of moving the object to be processed 92 and matchingan irradiation position of the laser light 14 emitted from the laserlight source 15 with an appropriate position. The laser light source 15may be moved instead of the XY stage 93. A sheath heater 94 for heatingthe object to be processed 92 is disposed inside the chamber 89. Theobject to be processed 92 corresponds to the bonded substrate 98. Thesheath heater 94 heats the substrate 83 m via the base body 82 in thebonded substrate 98. At the time, the sheath heater may be any heater aslong as the heater can heat the bonding substrate 98, and a halogenheater may be used instead of the sheath heater. Further, since thesubstrate 83 m is to be heated, the bonded substrate 98 may be heatedfrom the substrate 83 m side in the bonded substrate 98.

A window portion 95 is provided on one surface of the chamber 89. Thewindow portion 95 includes sapphire glass. An anti-reflective (AR)coating is applied to a surface of the sapphire glass. The laser lightsource 15 is installed outside the chamber 89, and the laser lightsource 15 irradiates the object to be processed 92 by the condensedlaser light 14. Since a material transparent with respect to the laserlight source 15 is suitable for the window portion 95, the sapphireglass is selected for the window 95.

In FIG. 26 , the bonded substrate 98 is installed in the chamber 89,vacuuming was performed, and the bonded substrate 98 is heated to apredetermined temperature T1 by the sheath heater 94. When a vacuumdegree is 100 Pa or less and a temperature of the substrate 83 m reachesT1 after waiting for 10 minutes or more, the first through hole 83 a andthe third recess portion 83 g on the angular velocity detection element3 side are irradiated by the laser light 14 and thereby melted. Sincethe temperature cannot be easily transmitted in a vacuum state, thetemperature T1 is preferably 300° C. to 400° C., which is relativelyhigh. The first through hole 83 a and the third recess portion 83 g formthe first melt portion 83 c.

Next, as shown in FIG. 27 , inert gas such as nitrogen gas is introducedinto the chamber 89 while the bonded substrate 98 is placed in thechamber 89, and the temperature of the bonded substrate 98 is controlledto T2. Since a thermal conductivity of the nitrogen gas is good when theair pressure in the chamber 89 is 100 Pa or more, the heatingtemperature may be 300° C. or less.

The second through hole 83 b and the fourth recess portion 83 h on theacceleration detection element 22 side are irradiated with the laserlight 14 and thereby melted. An irradiation energy may be lower thanthat in a case of the first through hole 83 a on the angular velocitydetection element 3 side. Therefore, dross, debris, cracks, and the likeare less likely to occur. The second through hole 83 b and the fourthrecess portion 83 h form the second melt portion 83 d.

After melting of all second through holes 83 b on the wafer iscompleted, a temperature in the chamber 89 is returned to a roomtemperature. The bonded substrate 98 is taken out from the chamber 89.

FIG. 28 shows a trajectory of the laser light 14. In the substrate 83 m,the first through holes 83 a and the third recess portions 83 g aredisposed on a plurality of parallel lines. The first trajectory 96 isalong a plurality of arrangements in which the first through holes 83 aand the third recess portions 83 g are disposed. In a step of formingthe first melt portion 83 c shown in FIG. 26 , the temperature of thebonded substrate 98 is maintained at T1, and the laser light 14 movesalong the first trajectory 96. The laser light 14 may be continuouslyirradiated on the first trajectory 96, or may be irradiated only whenthe laser light 14 passes through a region of the first through holes 83a and the third recess portions 83 g. That is, the laser light 14 may beradiated discontinuously in a pulsed manner on the first trajectory 96.

Similarly, in the substrate 83 m, the second through holes 83 b and thefourth recess portions 83 h are disposed on a plurality of parallellines. The second trajectory 97 is along a plurality of arrangements inwhich the second through holes 83 b and the fourth recess portions 83 hare disposed. In a step of forming the second melt portion 83 d shown inFIG. 27 , the temperature of the bonded substrate 98 is maintained atT2, and the laser light 14 moves along the second trajectory 97. Thelaser light 14 may be continuously radiated on the second trajectory 97,or may be radiated only when the laser light 14 passes through a regionof the second through holes 83 b and the fourth recess portions 83 h.That is, the laser light 14 may be radiated discontinuously in a pulsedmanner on the second trajectory 97.

In both the process of forming the first melt portion 83 c and theprocess of forming the second melt portion 83 d, the base body 82 isinstalled in the same chamber 89. The air pressure, the temperature, anda type of gas are changed. It takes time to change the inside of thechamber 89 from air pressure, normal temperature, and air topredetermined air pressure, temperature, and type of gas. Therefore, thefirst melt portion 83 c and the second melt portion 83 d can be formedwith higher productivity than in a method of taking out the bondedsubstrate 98 from the chamber 89 after the first melt portion 83 c isformed and putting the bonded substrate 98 into another chamber 89 toform the second melt portion 83 d.

As shown in FIG. 29 , the bonded substrate 98 is taken out from thechamber 89, and at least one side of the bonded substrate 98 is cut outby half dicing by using the dicing blade 18. In this way, the electrodepad 19 is exposed, and the wire bonding is possible. Thereafter, thefour sides of the bonded substrate 98 are cut, and the inertial sensor81 in which the angular velocity detection element 3 and theacceleration detection element 22 are mixedly mounted is completed. Areason why depths of the first melt portion 83 c and the second meltportion 83 d are different from each other is that laser irradiationenergies are different from each other.

Fourth Embodiment

In the present embodiment, an example of an inertial measurement unit2000 on which the angular velocity sensor 1, the acceleration sensor 21,or the inertial sensor 81 described above are mounted will be described.

The inertial measurement unit 2000 shown in FIG. 30 is a device thatdetects an inertial motion amount such as a posture or a behavior of amoving body such as an automobile or a robot. The inertial measurementunit 2000 is also referred to as an inertial measurement unit (IMU). Theinertial measurement unit 2000 functions as a so-called six-axis motionsensor including an acceleration sensor 21 that detects accelerationsAx, Ay, and Az in directions along three axes and an angular velocitysensor 1 that detects angular velocities ωx, ωy, and ωz around of thethree axes.

The inertial measurement unit 2000 is a rectangular parallelepipedhaving a substantially square planar shape. Screw holes 2110 are formedin the vicinity of vertexes at two locations located in a diagonaldirection of the square. The inertial measurement unit 2000 can be fixedto a mounted surface of a mounted body such as an automobile by passingtwo screws through the two screw holes 2110. It is also possible toreduce a size to a size that can be mounted on a smartphone or a digitalcamera, for example, by selecting a component or changing a design.

The inertial measurement unit 2000 includes an outer case 2100, abonding member 2200, and a sensor module 2300, and has a configurationin which the sensor module 2300 is inserted inside the outer case 2100with the bonding member 2200 interposed therebetween. The sensor module2300 includes an inner case 2310 and a substrate 2320.

Similarly to an overall shape of the inertial measurement unit 2000, theouter case 2100 has an outer shape of a rectangular parallelepipedhaving a substantially square planar shape, and the screw holes 2110 areformed in the vicinity of two vertices at two positions located in adiagonal direction of the square, respectively. The outer case 2100 hasa box shape, and the sensor module 2300 is accommodated inside the outercase 2100.

The inner case 2310 is a member that supports the substrate 2320, andhas a shape that fits inside the outer case 2100. The inner case 2310 isformed with a recess portion 2311 for preventing contact with thesubstrate 2320 and an opening 2312 for exposing a connector 2330.Thereby, the inner case 2310 is bonded to the outer case 2100 via thebonding member 2200. The substrate 2320 is bonded to a lower surface ofthe inner case 2310 via an adhesive.

As shown in FIG. 31 , a connector 2330, an angular velocity sensor 2340z that detects an angular velocity around a Z axis, an accelerationsensor unit 2350 that detects acceleration in each axial direction of anX axis, a Y axis, and the Z axis, and the like are mounted on an uppersurface of the substrate 2320. An angular velocity sensor 2340 x thatdetects an angular velocity around the X axis and an angular velocitysensor 2340 y that detects an angular velocity around the Y axis aremounted on a side surface of the substrate 2320.

The acceleration sensor unit 2350 can detect acceleration in one axialdirection, acceleration in two axial directions, or acceleration inthree axial directions, as necessary.

A control IC 2360 is mounted at a lower surface of the substrate 2320.The control IC 2360 that performs control based on a detection signaloutput from each sensor is a micro controller unit (MCU), includes astorage unit including a nonvolatile memory, an A/D converter, and thelike, and controls units of the inertial measurement unit 2000. Thestorage unit stores a program defining an order and a content fordetecting an acceleration and an angular velocity, a program fordigitizing detection data and incorporating digitized detection datainto packet data, accompanying data, and the like. A plurality ofelectronic components are mounted on the substrate 2320.

The angular velocity sensor 1 or the inertial sensor 81 is used for theangular velocity sensor 2340 z, the angular velocity sensor 2340 x, andthe angular velocity sensor 2340 y. The acceleration sensor 21 or theinertial sensor 81 is used for the acceleration sensor unit 2350.

Therefore, the inertial measurement unit 2000 includes the angularvelocity sensor 1, the acceleration sensor 21, or the inertial sensor 81described above. According to the configuration, the inertialmeasurement unit 2000 includes the angular velocity sensor 1, theacceleration sensor 21, or the inertial sensor 81 described above. Theangular velocity sensor 1, the acceleration sensor 21, or the inertialsensor 81 has a structure in which a crack is unlikely to occur in thelid body 4, the lid body 23, or the lid body 83. Therefore, the inertialmeasurement unit 2000 can be an inertial measurement unit 2000 includinga physical quantity sensor in which a crack is unlikely to occur in thelid body 4, the lid body 23, or the lid body 83.

Fifth Embodiment

In the first embodiment, the second recess portion 4 g is constituted bythe first groove 9 and the second groove 10 which are concentric withthe through hole 4 b in a plan view seen from the Z direction.

As shown in FIG. 32 , a through hole 200 corresponding to the throughhole 4 b in a plan view viewed from the Z direction may be a quadrangle.A recess portion 201 corresponding to the second recess portion 4 g in aplan view viewed from the Z direction may also be quadrangular. Therecess portion 201 is disposed in the periphery of the through hole 200.At the time, since a part of the laser light 14 is diffracted in therecess portion 201, the laser light 14 travels in multiple directions inthe periphery of the through hole 200. Therefore, since a change in theresidual stress at the melt portion 4 c is gentle, an occurrence ofcracks can be inhibited. In addition, a shape of the through hole 200and the recess portion 201 in a plan view viewed from the Z directionmay be a rhombus, a triangle, or a checkered pattern.

As shown in FIG. 33 , a through hole 210 corresponding to the throughhole 4 b in a plan view viewed from the Z direction may be a quadrangle.A recess portion 211 corresponding to the second recess portion 4 g in aplan view viewed from the Z direction may have a radial rectangularshape extending from the through hole 210. The recess portion 211 isdisposed in the periphery of the through hole 210. At the time, since apart of the laser light 14 is diffracted in the recess portion 211, thelaser light 14 travels in multiple directions in the periphery of thethrough hole 210. Therefore, since a change in the residual stress atthe melt portion 4 c is gentle, an occurrence of cracks can beinhibited. In addition, the recess portion corresponding to the secondrecess portion 4 g in a plan view viewed from the Z direction may have aspiral shape.

What is claimed is:
 1. A physical quantity sensor comprising: a movablebody; a base; and a lid, wherein the movable body is housed in a spacebetween the base and the lid, the space is sealed by sealing a throughhole provided in the lid with a melt portion, the melt portion issubstantially circular in a plan view, and includes a continuous curvedsurface including unevenness, and a center of the curved surface isconcave in a cross-sectional view.
 2. The physical quantity sensoraccording to claim 1, wherein the lid is formed of a single crystalmaterial, and the melt portion is polycrystalline.
 3. The physicalquantity sensor according to claim 1, wherein the lid is formed ofsilicon.
 4. The physical quantity sensor according to claim 1, whereinthe melt portion is formed by irradiating a plurality of concentricgrooves formed around the through hole of the lid with a laser beam tomelt the lid.
 5. The physical quantity sensor according to claim 1,wherein a first surface of the lid faces the base, a second surface ofthe lid is opposite to the first surface, and0.50≤D/L≤3.00, wherein D is a length from the second surface to an endof the melt portion nearest the first surface, and L is a diameter ofthe melt portion nearest the second surface in the plan view.
 6. Thephysical quantity sensor according to claim 5, wherein0.01≤D/L≤0.50.
 7. The physical quantity sensor according to claim 1,wherein a pressure of the space is 0.1 Pa to 10 Pa.
 8. The physicalquantity sensor according to claim 1, wherein a pressure of the space is10,000 to 150,000 Pa.
 9. The physical quantity sensor according to claim1, wherein the space is filled with an inert gas.
 10. The physicalquantity sensor according to claim 9, wherein the inert gas is nitrogenor argon.
 11. The physical quantity sensor according to claim 1, whereinthe space is subjected to a hydrophobic treatment, and a moisturecontent of the space is 100 ppm or less.
 12. An inertial measurementunit comprising: a physical quantity sensor according to claim 1; and amicro controller that performs control based on a detection signaloutput from the physical quantity sensor.